eComment: Pharmacological agents increasing arterial pressure via total peripheral vasoconstriction should be avoided for maintaining brain oxygenation during cardiac displacement in off-pump cardiac surgery

We read with great interest the manuscript by Atasever et al. [1] recently published in this journal. The authors reported important insights into the influence of manipulating the heart on microcirculatory perfusion and brain oxygenation in off-pump coronary artery bypass grafting surgery. Cardiac displacement was associated with a reduction in cardiac output, mean arterial pressure as well a reductions in sublingual microcirculation (capillary red blood cell velocities) and near-infrared spectroscopy derived cerebral tissue oxygenation index. Also, repositioning the heart in its original position restored all variables to baseline values and patients were discharged from the intensive care unit within 24 h of surgery without any adverse postoperative cerebrovascular accident. These results suggest that a reduction in cardiac output lowers sublingual tissue perfusion and oxygenation and brain tissue oxygenation within that specific clinical situation. In regards to the latter, this study adds valuable information to the existing link between changes in cardiac output and cerebral blood flow/oxygenation in different circumstances. Atasever et al. [1] state that their findings warrant pharmacological and surgical strategies for maintaining the systemic circulation during cardiac displacement in off-pump cardiac surgery. While we agree with their conclusion, we would like to underline the fact that not every pharmacological strategy to increase perfusion pressure will be beneficial for brain oxygenation. Recent evidence, including data from of our laboratory, suggests that the utilization of phenylephrine and norepinephrine leads to a reduction in frontal lobe oxygenation. In normotensive healthy conscious subjects, our group [2] and others have reported a reduction in frontal lobe oxygenation with infusion or bolus injections of phenylephrine. In addition, we [3] and others [4] have also reported a lowering in cerebral oxygenation following administration of phenylephrine in anesthetized patients undergoing elective surgery and experiencing anesthesia-induced hypotension. A restraint in frontal lobe oxygenation by phenylephrine may have been established directly through a pharmacological effect or a reflex elevation in cerebral vascular resistance triggered by the increase in arterial pressure, supported by a low cardiac output [4]. Also, continuous infusion of increasing doses of norepinephrine reduced middle cerebral artery mean flow velocity and cerebral oxygenation estimated by frontal lobe oxygenation and internal jugular venous oxygen saturation in normotensive healthy subjects [5]. Conversely, ephedrine increases mean arterial pressure mainly by elevating cardiac output, without any influence on cerebral perfusion in normotensive healthy subjects. Finally, frontal lobe oxygenation is maintained when ephedrine is used to restore mean arterial pressure in patients undergoing elective surgery and experiencing anesthesia-induced hypotension [3, 4]. Taken together, these findings suggest that special attention is required when deciding which pharmacological strategy should be used to secure cerebral perfusion pressure in clinical situations such as during cardiac displacement in off-pump cardiac surgery. Indeed, some agents could eventually be more harmful than beneficial for the brain.

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